Lviv MD Day 2015 Павло Захаров "Reactive cocoa: paradigm shift"

Pavlo Zakharov
Reactive Cocoa:
Paradigm shift.
- What is Reactive functional Paradigm?
- Why consider using ReactiveCocoa?
- RAC Signal.Unifying all of Cocoa’s common
patterns.
- RAC and concurrency.
- Implementing MVVM design pattern on iOS
with RAC.

What is Reactive Functional
Programming?

Functional reactive programming (FRP) is a programming paradigm for
reactive programming (asynchronous dataflow programming) using the building
blocks of functional programming (e.g. map, reduce, filter). FRP has been used for
programming graphical user interfaces (GUIs), robotics, and music, aiming to
simplify these problems by explicitly modelling time. (c) Wikipedia

Reactive+Functional:
❖ Static/Dynamic data flow.(Programming based on
Events)
❖ (Functional Blocks) Functions passed as arguments to
functions.

Cocoa Events
❖ Delegation
❖ KVO
❖ Target - Action
❖ Callback Blocks
❖ NSNotifications
}RacSignal

RACSignal
❖ Next
❖ Error
❖ Completed
Ray Signal emits:
[self.searchText.rac_textSignal subscribeNext:^(id x) {
NSLog(@"Next ocured");
}error:^(NSError *error) {
NSLog(@"Error ocured");
}completed:^{
NSLog(@"Completed");
}];
Signal can have one or multiple subscribers

Events
Event flow:
CompletedCompleted
NextNext
NextNext
NextNext ErrorError
NextNext NextNext …

Reactive Operations
❖ Map
❖ Throttle
❖ Skip
❖ Filter
❖ DeliverOn
❖ more…

Operations don’t care about
signal source.

Map
❖ Transforms the value of the event(As transformed value
as input signal can be literally anything)
RACSignal *mySignal = [textSignal map:^id(NSString *text) {
return @(text.length>3);
}];
[mySignal subscribeNext:^(NSNumber* x) {
if ([x boolValue]) {
//...
}
}];

Combine
❖ Combines two RAC Events(Next Emits when one of
combined events occurs).
RACSignal *switch1Signal = …
RACSignal *switch2Signal = …
RACSignal *both = [RACSignal combineLatest:@[switch1Signal,switch2Signal] reduce:^id(NSNumber *switch1,
NSNumber *switch2){
return @([switch1 boolValue] && [switch2 boolValue]);
}];
[both subscribeNext:^(id x) {
if([x boolValue]){
NSLog(@"Both");
}
}];

Filter
❖ Event will be emitted only if the condition is satisfied.
[[self.usernameTextField.rac_textSignal filter:^BOOL(id value) {
return (((NSString*)value).length>3);
}]subscribeNext:^(id x) {
NSLog(@"do stuff");
}];

Throttle
❖ If event occurrence once more within time interval
specified event wouldn’t be emitted.(Extremely useful
for locking buttons to prevent speed clicking)
[[[self.usernameTextField.rac_textSignal filter:^BOOL(id value) {
}]throttle:0.5]subscribeNext:^(id x) {
NSLog(@"do stuff");
}];

Deliver On
❖ The block will be executed on thread specified (For
example for UI stuff on main thread)
[[[self.usernameTextField.rac_textSignal filter:^BOOL(id value) {
}] deliverOn:[RACScheduler mainThreadScheduler]]subscribeNext:^(id x) {
NSLog(@"do UI stuff");
}];

How to mix reactive code with
non-reactive?

Option one: doNext block
❖ doNext Block will be executed before subscriberBlock
will be called.This is the good place for reactive code.
[[[self.signInButton
rac_signalForControlEvents:UIControlEventTouchUpInside]
doNext:^(id x) {
//put your non-reactive code here
}]
subscribeNext:^(NSNumber *signedIn) {
//do stuff
}];}

Wrap non-reactive code to
reactive
❖ Method will create signal which can emit
next/error/completed event based on your non-
reactive conditions.
-(RACSignal *)switchSignal{
return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
(self.switch1.isOn)?[subscriber sendNext:@(YES)] : [subscriber sendNext:@(NO)];
return nil;
}];
}
//.
//.
//.
[[self switchSignal]subscribeNext:^(id x) {
//doStuff
}];

Bind Signal to UIEvent
❖ Every time touchUpInside event occurs next event will
be emitted;
RACSignal *mySignal = [self.getButton rac_signalForControlEvents:UIControlEventTouchUpInside]

Avoid Retain cycles
❖ Accessing self in block can cause retain cycle and
memory leak.Use __weak self to prevent it.
@weakify(self);
[self.searchText.rac_textSignal subscribeNext:^(id x) {
@strongify(self);
// self.smth = smth
}error:^(NSError *error) {
@strongify(self);
// self.smthElse = smth
}completed:^{
@strongify(self);
// self.smthReallyDifferent = smth
}];

ViewModel
❖ ViewModel which is a special type of model that
represents the UI state of the application
ViewView ViewModelViewModel ModelModel
ViewView ViewModelViewModel ModelModelControllerController

Binding
❖ Binds textField.text to the property in ViewModel.
Every time property changes text will change as well.
(WPF implementation is shown on the right)
RAC(self.searchText,text) =
self.myString;
<TextBlock TextContent=”{Binding
Path=Description}” />
~

Why should i use RAC?
❖ Unified interface for all Cocoa events.
❖ Less code in comparison with non-reactive code.
❖ No massive ViewControllers with complicated
relationships.
❖ Easy work with concurrency.
❖ No complicated “States” needed.

Some Disadvantages
❖ Debug Hell.
❖ Little overhead
❖ Weird syntax.(But you will get used to it)

Resources
❖ https://github.com/ReactiveCocoa/ReactiveCocoa
❖ http://www.raywenderlich.com
❖ http://blog.scottlogic.com/2014/07/24/mvvm-reactivecoc
❖ https://www.youtube.com/watch?v=DgdISd1Qc48
❖ https://www.youtube.com/watch?v=fWV7xyN5CR8
❖ https://github.com/ZakharovPaul/RacDemo.git

Thank you
Skype: c1ark.
E-mail:
zakharov.paul@live.com

Lviv MD Day 2015 Павло Захаров "Reactive cocoa: paradigm shift"

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Lviv MD Day 2015 Павло Захаров "Reactive cocoa: paradigm shift"